Reversing control system for electrically powered vehicles

ABSTRACT

A control system for effecting reversal of electrically powered vehicles, typically heavy duty off-road type work vehicles having electric motor driven wheels, characterized as follows: (1) a reversing switch is actuated, or reversed, in response to speed of at least one wheel motor below a predetermined speed, without requiring waiting for reversal of polarity on the power buses; (2) a reversing switch is reversed in response to the speed of the slowest turning of two wheel motors, one on each side of the vehicle to effect uniform reversal of the vehicle, regardless of whether it is in a turn in either direction or moving straight ahead, and without requiring waiting for reversal of the polarity on the power buses; and (3) a reversing switch is actuated when the voltage drop across a slowest turning motor becomes low enough to operate a current sensitive relay connected with the reversing switches, the two wheel motors being connected such that there is no cross feed therebetween and in bucking relationship with a regulated voltage source to effect optimal response. Also disclosed are specific structure, interconnection, and operational details.

Friend et al.

States atent 1191 1451 Mar. 19, 1974 i 1 REVERSING CONTROL SYSTEM FORELECTRICALLY POWERED VEHICLES 57 T T lnvemofsi Aaron y Nelson; A controlsystem for effecting reversal of electrically Royce Yoder, 8110fLongview, powered vehicles, typically heavy duty off-road type T workvehicles having electric motor driven wheels, [73] AssigneeZ R.LeToumeau, hm9 Longview, characterized as follows: (1) a reversingswitch is actuated, or reversed, in response to speed of at least onewheel motor below a predetermined speed, with- Filedi y 3, 1971 outrequiring waiting for reversal of polarity on the [21] Appl No: 139,659power buses; (2) a reversing switch is reversed in response to the speedof the slowest turning of two wheel motors, one on each side of thevehicle to effect Cl 318/56, 318/i58 uniform reversal of the vehicle,regardless of whether [51] Int. Cl. it is in a turn in either directionor moving traight Field of Search 318/52, 71, 55, 56, 158 ahead, andwithout requiring waiting for reversal of the polarity on the powerbuses; and (3) a reversing References Cited switch is actuated when thevoltage drop across a UNITED STATES PATENTS slowest turning motorbecomes low enough to operate 3,109,972 11/1963 Edwards 318/55 8 currentSensitive relay Connected with the reversing 3'1g3990 5/1965 Edwardsllll n 3i8/56 x switches, the two wheel motors being connected such2,962,642 11/1960 Brane 318/55 that there is no cross feed therebetweenand in buck- 2,565.293 8/1951 Aydelott et al. 318/55 ing relationshipwith a regulated voltage source to ef- 2,3l5.386 3/1943 Baldwin 318/71 Xfeet optimal responge Also disclosed are pecific structure,interconnection, and operational details.

P r -vqm n ilisfiakx hs 5 Claims, 2 Drawing Figures Felsman & Fails sPED 7 55 49 6.9 ahib 69 57 53 612- 78 m' l I i g wa a es f M MEANS 5b bs-CONTROL 29 VOLTAGE MOTOR L 29 SOURCE EXCITER a9 REVERING 1/1 10.9 sggi'g RE aa e gl r qs N WIT H 47. 1131115111115 CONTROLLER ENGINE SOURCEMEANS 56 1 1/9 42/ J 1 i i 27 r .e 5 RESIS'ADNCE -73 GENERATOR GENERATORMOTOR "-1a RESLIJFIQNCE MEANS EXCITER EXCITER d [FANS 47v 2 1/6 //7 h t.9/ 1 -99 r\ t\ 57 K L 5 i N95 L a /05 /0/ 55 i RESSJgNCE RESISR'FSNCE 1H J r s MEANS 6,5 57 MEANS 5.9 5/" sb SPEED 5 SENSING MEANS I HaREVERSING CONTROL SYSTEM FOR ELECTRICALLY POWERED VEl-HCLES BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates tocontrol systems for electrically powered vehicles; and, moreparticularly, to reversing control systems for controlling vehicleswherein the vehicle wheels are driven by electric motors which aresupplied power from one or more generators, which are in turn powered byone or more prime movers such as internal combustion engines.

2. Description of the Prior Art Many types of control systems have beendevised in the prior art for various applications involving vehiclesdriven by electric traction motors supplied power from internalcombustion driven generators, a notable example being diesel-electrictrains. Although the general concept is quite old, the particular typeapplication with which this invention is primarily concerned isrelatively new insofar as actual practice is concerned. This applicationis that of the heavy duty type self-propelled, rubber-tired, off-roadvehicle and/or mobile selfpropelled work performing machine. Machines ofthis general class include, by way of example, off-road transportvehicles; earth moving and earth working machines such as scrapers,dozers, tractors and haulers; land clearing machines; logging machines;mobile cranes; heavy duty cranes or hoists. It is only recently thatsuch machines have been electrically powered to a practical commercialextent; that is, having an internal combustion engine or engines drivinga generator or generators to supply electrical power to vehicle wheelmotors as well as to the other functions of the machine. Therequirements for the electrical systems of such machines are quitesevere. The electrical system of such machines must cope with wheelmotor load and speed changes that are quite rapid and extend over a widerange. Further, it is very important that such machines have aneffective dynamic braking system, since the braking demands are much toosevere for frictional brakes alone.

U.S. Pats. Nos. 3,102,219, 3,417,304 and 3,492,556 disclose controlsystems for electrically powered vehicles of the type hereinbeforereferred to. Improved vehicle control systems as well as improveddynamic braking systems have made desirable the anticipation and earlyswitching of the reversing switch means to effect reversal of directionof a vehicle. Moreover, it was desired to effect a reversal that wassubstantially uniform so that the operator could judge the response ofthe vehicle, regardless of whether the vehicle was in a turn or movingstraight ahead. Furthermore, the anticipatory reversal system effectingthe uniform reversal of the vehicle needed to be as simple, compact andreliable as possible. Since this class of machines is relatively new,the prior art has not afforded adequate solutions to these needs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block schematic diagramshowing apparatus, control systems and arrangements in accordance withone embodiment of this invention.

FIG. 2 is a partial schematic circuit diagram of one embodiment of thisinvention useful in the embodiment of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS It is a general object of thisinvention to provide control apparatus, systems, and arrangements whichwill result in improved performance in reversing the direction of travelof vehicles of the general class abovementioned.

It is an object of this invention to provide a reversing control systemthat reverses when the speed of the vehicle gets below a predeterminedspeed to provide a sort of preact and effect a faster reversaloperation. Specifically, it is an object of the invention to accomplishthe reversal when the speed of the slowest wheel of a pair of wheelsdisposed on opposite sides of the vehicle get below the predeterminedspeed.

It is an object of this invention to effect the reversal in response tovehicle speed by the use of a reversal system that is as simple, compactand reliable as possible.

These and other objects will become apparent to one skilled in the artwhen the following descriptive matter is read in conjunction with thedrawings.

The term vehicle is used herein to include any vehicle to which thepresent invention is applicable, in addition to the wheel vehicles thatare specifically discussed herein with reference to the description ofpreferred embodiments of this invention.

Referring to FIG. 1, there are shown four direct current traction ordrive motors 11, 13, 15 and 17. These motors are incorporated intoself-contained vehicle wheel drive units. Such wheel drive units includea gear reduction unit built into the wheel structure, with the tractionmotor driving the gear reduction unit. The wheel drive units are thenmounted to the vehicle axles. For details of such wheel drive units(sometimes referred to as electric wheels) reference is made to US. Pat.No. 2,726,726. For purposes of discussion herein, the wheeled vehicle ofthe illustrated preferred embodiments will be assumed to have fourwheels, each of which is an electric wheel. It should be understood,however, that the present invention is applicable also to wheeledvehicles having either less or more than four electric wheels, as wellas to pertinent vehicles that are not wheeled; for example, hoists.

Also shown in FIG. 1 are a generator 19, a generator exciter 21 and amotor exciter 23, all driven by an internal combustion engine 25 viaconventional mechanical linkages, indicated by the dashed lines 27.While only one engine and generator are shown, the present invention isalso applicable in cases where more than one engine-generator set isused. The present invention is also applicable in some of its aspects tovehicles wherein the prime mover power source is other than an internalcombustion engine; for example, a turbine. The prime mover power sourcecould in some applications be located remotely from the vehicle. Thegenerator is preferably either a shunt type generator or a differentialcompound type generator. The generator has, of course, output terminals.Each of the direct current traction motors is preferably of thecumulative compound type, having an armature 29, a series field winding31, a shunt field winding 33, and input terminals.

One output terminal of the generator 19 is connected via lead 37 to afirst main line bus 39 and the other output terminal of the generator 19is connected by a lead 41 with a second main line bus 43.

The left front wheel motor 13 has one side of its armature 29 connectedvia lead 45 to the first main line bus 39, and the right front wheelmotor 11 has a corresponding side of its armature 29 connected via lead47 with the first main line bus 39. The right and left front wheelmotors 11 and 13 have their respective other side of their armatures 29connected via respective leads 49 and 51, and reversing switch means 53with the other main line bus 43.

Similarly, the left rear wheel motor 17 has one side of its armature 29connected via lead 55 with the first main line bus 39, and the rightrear wheel motor 15 has a corresponding side of its armature 29connected via lead 56 with the first main line bus 39. The right andleft rear wheel motors 15 and 17 have their respective other side oftheir armatures 29 connected via respective leads 57 and 59 andreversing switch means 61 with the other main line bus 43.

In brief, the front wheel motors 11 and 13, the rear wheel motors l and17, and the output terminals of the generator 19 are all connected inparallel across the main line buses 39 and 43. Further, the serieswindings 31 of all of the wheel motors are arranged to be reversed byaction of the respective first and second reversing switch means 53 and61. Suitable reversing switch means and the interconnection of theirrespective contacts with the motors and their series fields areillustrated in the U.S. Pats. Nos. 3,102,217; 3,417,304; and 3,492,556,referenced hereinbefore. Any of the arrangements of the respectivereversing switch means and the series fields 31 described in theabovereferenced patents may be employed herein.

Referring to FIG. 1, each of the reversing switch means 53 and 61 isconnected with an actuation means 75 that is linked to the respectivereversing switch means, as shown by the lines 78. For example, theactuation means 75 may comprise a current sensitive relay", illustratedas the block 139, FIG. 2. The current sensitive relay 139 is linked torespective contact set for each of the motors for which that reversingswitch means serves. Each contact set is, in effect, a double poledouble throw reversing switch.

In this invention, the actuation means 75 is actuated responsive to thespeed of the vehicle to effect a faster reversal operation.Specifically, the actuation means 75 is connected with a speed sensingmeans 65 by suitable leads, illustrated as conductor 67. The speedsensing means 65 is responsively connected with at least one motor suchas motor 15, as indicated by dashed line 71. As illustrated in FIG. 1,the actuation means 75 is connected via the respective speed sensingmeans with at least two wheels, one on each side of the vehicle. In thisway, the slowest turning wheel motor will effect actuation of theactuation means 75, regardless of whether the vehicle is turning to theright, turning to the left, or moving straight ahead. Such uniformity ofoperation of the vehicle in reversal of direction is desirable in orderthat the operator gets a feel for the vehicle and not experience adifferent sensation for each operating condition of the vehicle. Thespeed sensingmeans .65 may be a tachometer-generator or the like that ismechanically coupled with the respective wheel motor and generates anoutput voltage in response to the speed of revolution of the wheelmotor. In such an event, the actuation means may be activated when thevoltage output of the tachometer-generator becomes low enough.

Preferably, however, a speed sensing means 65 and an actuation means asillustrated in reversing control system of FIG. 2 are employed. Thesystem of FIG. 2 will be described in detail after the remainder of theoverall control system of FIG. 1 is described.

In the overall control system of FIG. 1, a plurality of dynamic brakingresistance grid means are serially connected with the respective wheelmotors for dissipating power developed by the motors when they areacting as respective generators to effect dynamic braking of thevehicle. The resistance grid means 81, 83, 85, and 87 are connectedserially with the armatures 29 of the respective wheel motors 11, 13, 15and 17 across the main line buses 39, 43. As illustrated, respectiveseries circuits may be traced from the first main line bus 39, throughthe armatures of the respective wheel motors, the respective leads 49,51, 57 and 59, and the respective resistance grid means. For example,the resistance grid means 81 is serially connected with the lead 49,from the other side of the armature 29 of wheel motor 11, via lead 89;and with main line bus 43 via lead 91. Similarly, the resistance gridmeans 83 is serially connected with lead 51 and the main line bus 43 vialeads 93 and 95; the resistance grid means 85 is serially connected withthe lead 57 and the main line bus 43 via leads 97 and 99; and theresistance grid means 87 is serially connected with the lead 59 and themain line bus 43 via leads 101 and 103. As can be seen in FIG. 1, therespective resistance grid means are also connected in parallel with therespective reversing switch means and the respective series fieldwindings 31 such that the resistance grid means are effectively shuntedby the series field windings 31 during normal dirving operation.

Referring to FIG. 1, a controller 105 is connected with a generatorexciter control voltage source 107 and with the generator exciter 21 viarespective leads 109 and 111, and 113 and 115 for control of thevehicle. As described in the cited Pat. No. 3,492,556, the controllermay be a potentiometer that is arranged to have a voltage output that iscontinuously variable from zero up to a predetermined magnitude, bothpositive and negative. The controller may be operated manually in bothdirections or by a combination of foot-operated accelerator pedal and areversing control switch at the operators console. If desired, aninterlock arrangement can be employed to prevent effective operation ofthe reversing control switch until the accelerator pedal is returned toits neutral, or idling, position. The controller is operable to provideexcitation of the generator exciter 21. The generator exciter 21 is, inturn, connected with the generator 19 via leads 1 16 and l 17 forcontrolling the output of the generator. The generator exciter controlvoltage source 107 will have several inputs from different sources,depending upon the degree of automationthat is designed into the overallcontrol system. For example, any of the controllers and generatorexciter control voltage sources employed in either of the cited U.S.Pat. Nos. 3,102,219; 3,417,304; and 3,492,556 may be employed with thisinvention. Any other satisfactory generator exciter control voltagesource and controller may be employed. It is sufficient herein to notethat the controller 105 is operable by the operator of the vehicle tocontrol forward and reverse direction and speed of the vehicle.

For control of the speed of the vehicle, a motor exciter control voltagesource 123 is provided, which is connected with the motor exciter 23 vialeads 119 and 121. The motor exciter control voltage source, will have aplurality of inputs, depending upon the degree of automation that isdesigned into the overall control system. One suitable and relativelysimple motor exciter control voltage source is described in the citedPat. No. 3,102,219. Other suitable but more complex motor excitercontrol voltage sources that employ inputs from a plurality of sensedvariables, are described in the cited Pat. Nos. 3,417,304 and 3,492,556.Any other satisfactory motor exciter control voltage source may beemployed. It is sufficient herein to note that the motor exciter controlvoltage source is operable to bring the vehicle speed to the speedsignalled by the operator.

The output of motor exciter 23 is connected with the shunt fieldwindings 33 of the respective wheel motors; as indicated by the leads aand b, drawn discontinuous for simplicity. The motor exciter 23 thuscontrols the speed of the wheel motors.

As indicated hereinbefore, a preferred form of the actuation means 75and the speed sensing means 65 is illustrated in FIG. 2, wherein theactuation means 75 may be considered the portion enclosed by dottedlines and the speed sensing means for one wheel motor may be consideredthe conductors 57, 58, 56, 39 and the speed sensing means for the otherwheel motor 17 may be considered the conductors 59, 60, 55, 39. In FIG.2 are illustrated serially connected regulated voltage power source 135,unidirectional conductor means 137, current sensitive relay 139, bridgemeans 141, switch means 143 and two parallel connected armatures 29 ofwheel motors 15 and 17. The wheel motors 15 and 17 have one sideconnected with the first main line bus 39 via leads 55 and 56, asillustrated in FIG 1. Similarly, the other side of the motors 15 and 17are connected with the other main line bus via leads 57 and 59 andreversing switch means 61.

The regulated voltage power source 135 is connectable in buckingrelationship with the voltage drop across the armatures of the wheelmotors l5 and 17. Basically, the regulated voltage power sourcecomprises an isolation transformer 147; a full wave rectifier 149connected with the isolation transformer for producing unidirectionalcurrent flow; and parallelcoupled ripple filter means 151 and zenerdiode means 153 for maintaining a regulated voltage. The regulatedvoltage power source 135 provides a voltage at its output terminals thatis equal to the sum of the voltage drop across a respective wheel motorarmature at a predetermined low speed at which it is desired to effectreversal of the reversing switch means and the voltage drop across thecurrent sensitive relay when the minimum current sufficient to effectactuation thereof is flowing therethrough. It has been found forexample, that a voltage supply of about 75 volts affords a satisfactoryvoltage output of the regulated voltage power source. Specifically, theoutput of the isolation transformer 147 is serially connected viavoltage dropping resistor 155 and leads 157 and 159 with the inputterminals of the full wave rectifier 149. As illustrated, the full waverectifier 149 comprises a diode bridge, although any other satisfactoryfull wave rectifier may be employed. As illustrated, the outputterminals of the full wave rectifier are connected in parallel with aripple filter comprising parallel-coupled capacitor 161 and resistor163. Also coupled in parallel with the ripple filter are a plurality ofserially connected zener dimeans 143, bridge means 141, parallelconnected armatures of motors 15, 17 and current sensitive relay 149.The diode 137 and bridge 141 prevent reverse current flow, andspecifically prevents current from flowing through the current sensitiverelay when the armature voltage of either wheel motor exceeds thevoltage of the regulated voltage power source.

The current sensitive relay 139 has a fixed resistance and a biasingmeans such that the relay will be actuated when a predetermined currentflows therethrough, as when a predetermined voltage drop is effectedacross the relay. For example, it has been found satisfactory to employa relay that will operate when about 3 milliamperes of current flowstherethrough, requiring a voltage drop of about 45 volts across therelay. If desired, a series resistance-capacitance network may beemployed in parallel with the relay to alleviate problems with the noisespikes caused by closing or opening of the contacts of the reversingswitch means, actuated by the current sensitive relay 139.

The bridge means 141 will select the slowest motor to be seriallyconnected into the circuit in bucking relationship with the regulatedvoltage power source 135. The bridge means 141 has four legs, twoadjacent legs 169 and 171 on one side and two adjacent legs 173 and 175on the other side. The juncture of the two adjacent legs; for example,169 and 171; define input terminals 177 and 179. The juncture ofthefirst legs 169 and 173 define an output terminal 181, whereas thejuncture of the second legs 171 and 175 define a second output terminal183. The first leg, such as leg 169, of a respective side of the bridgehas a unidirectional conductor means for current flow in one directionwith respect to the input terminal of that side, and the second of theadjacent legs has a unidirectional conductor means for permittingcurrent flow in the other direction with respect to the input terminalon that side. As illustrated, the unidirectional conductors are diodes,appropriately poled. Thus, it can be seen that the bridge means 141comprises a diode bridge means which allows current flow in eitherdirection through both motors, but which will automatically select thepath of the slowest turning motor; that is, the motor having the lowestbucking voltage output thereacross; to connect in series with theregulated voltage power source 135, the diode 137 and the currentsensitive relay 139. The diodes in the legs of bridge means 141 alsoserve to isolate the respective motors to prevent cross feedtherebetween.

The switch means 143 serves to maintain the regulated voltage powersource 135 connected in a signalled bucking relationship with the wheelmotor outputs l5 and 17 regardless of the direction of travel of thevehicle. The switch means comprises a first group of switches 187a, 187band 1870; and a second group of switches 189a, 18% and 189C. The firstgroup of switches 187a-c are responsively connected as shown by thedashed line 191 with a controller means such as controller for seriallyconnecting a first output terminal such as output terminal 183 of thebridge means 141, the wheel motors l5 and 17, the regulated voltagepower source 135, and the current sensitive relay 139 for current flowin one direction through the wheel motors. The second group of switches189a-c are responsively connected, as shown by the dotted line 193 withthe controller 105 for serially connecting a second output terminal 181of the bridge means, the wheel motors and 17, the regulated voltagepower source 135 and the current sensitive relay 139 for current flow ina second direction through the wheel motors. When the first group ofswitches l87a-c is closed, a circuit may be traced from one outputterminal of the regulated voltage source 135 via diode 137, switchesl87b and 187C to terminal 183 and from terminals 177 and 189 througharmatures of respective motors 15, 17 to bus 39, and from bus 39 viaswitch 187a and current sensitive relay 139 to the other output terminalof the regulated voltage source 135. When the second group of switches189a-c is closed, a circuit may be traced from one output terminal ofthe regulated voltage source 135 via diode 137 and switch l89b to bus 39and from bus 39 through armatures of respective motors 15, 17 toterminals 177, 179 and from terminal 181 via switches 189C and 189a andcurrent sensitive relay 139 to the other output terminal of theregulated power source.

Operation of the electrically powered vehicle control system inaccordance with this invention will now be explained. The positions ofthe controls as shown in FIG. 1 represent the condition wherein thevehicle is parked and ready for movement in the forward direction. Theelectric wheel motors of the vehicle are preferably provided withelectromagnetic friction brakes (not shown) of a type which may be setor released by the vehicle operator, as desired, and particularly forparking the vehicle.

Vehicle Forward Operation Assuming that the vehicle engine 25 is runningand that it is desired to move the vehicle forward, it is only necessaryto move the controller 105 away from its neutral position in the forwarddirection a desired amount. A direct current voltage of proper polaritywill immediately be applied to the field of the generator exciter 21;which, in turn, will cause the generator exciter to supply directcurrent voltage of proper polarity to the generator shunt field,whereupon the generator output voltage will appear across the main linebuses 39 and 43. The main line bus voltage (generator output voltage) isof course applied to the armatures of all of the wheel motors.

The wheel motor shunt fields 33 are supplied direct current voltage fromthe output of the motor exciter 23 via leads a and b. For additionaldetaisl as to the motor excitation control system, reference is made tothe cited Pat. Nos. 3,093,780 and 3,102,219.

Thus, with armature voltage and shunt field excitation applied to themotors, the vehicle will move forward. Assuming that the vehicleinitially is lightly loaded, the generator maximum voltage output willbe relatively high, the motor shunt field excitation will be relativelylow, allowing the vehicle to run under what might be termed high speed,low torque conditions. For the initially assumed light load condition,the further the main controller 105 is advanced away from neutral, thefaster the vehicle will travel. With the controller 105 fully advanced,the generator output will be maximum and the motor shunt fieldexcitation will be minimum. and the vehicle speed will be maximum. Themotor exciter may be provided a pilot shunt field (not shown) to preventcomplete collapse of the motor shunt fields. When the vehicle isoperating under heavy load conditions, the generator maximum outputvoltage is reduced, resulting in high motor shunt field excitation. Thismay be termed the low speed, high torque operating condition. To stopthe vehicle forward motion, it is only necessary to return thecontroller to its neutral position.

Vehicle Dynamic Braking Operation Dynamic braking action isautomatically efiected when the wheel motors exceed the signalled speedof operation of the vehicle. The dynamic braking action is controlled byoperation of the controller 105. The detailed circuits and operation oftypical suitable controllers have been described particularly inreferenced Pat. Nos. 3,102,219 and 3,417,304, and do not, per se, form apart of this invention. Accordingly, no detailed description is hereinincluded. Briefly stated, however, a dynamic braking signal effectsreduction of the generator exciter shunt field. The motor series fields31 are rendered inactive by diodes 69 during the dynamic brakingoperation, since the series fields 31 are in bucking relation to theshunt fields 33 during dynamic braking and otherwise would decrease theeffectiveness of the motors when they are acting as generators. Thepower generated by the wheel motors during dynamic braking is dissipatedby the respective resistance grid means 81, 83, 85 and 87; and by thegenerator 19, which is now acting as a motor driving internal combustionengine 25. The efficiency of the generator 19 as a motor is such that itwill drive the load provided by the internal combustion engine 25 withina narrow range of speed near the normal engine operating speed. Thismeans that the engine is ready at all times to immediately pick up itsgenerator load when the dynamic braking signal is removed.

The respective resistance grid means are connected in series with thewheel motors, now acting as generators, to begin immediate dissipationof the energy of dynamic braking to minimize a tendency to overdrive thegenerator 19 in the internal combustion engine 25.

The dynamic braking is effective, not only in forward operation but alsoin reverse operation.

Vehicle Reverse Operation To move the vehicle in the reverse direction,it is only necessary to move the controller away from its neutralposition in the reverse direction a desired amount. Tis will cause avoltage of opposite polarity to be applied to the generator exciter 21;which will, in turn, apply the voltage of opposite polarity to thegenerator shunt field, causing the generator output voltage to reverseits polarity. The vehicle can, of course, go to the reverse direction ofoperation from a standstill, but can also go from forward operation toreverse operation and vice versa.

Assume the vehicle is moving forward in a turn to the left and it isdesired to reverse the direction of travel. The operator signals thereversal of the machine; as by moving a control lever in a reversedirection, or by flicking a reversing switch to reverse position andallowing the accelerator pedal to return to the neutral position. Thiseffects closure of the switches 187a-c, as illustrated in FIG. 2. Theleft wheel motor 17 is the slowest turning motor in the left turn. Aslong as the voltage sensed by the input terminal 179, and consequently,the bucking terminals and 167, is too high, there will be inadequatecurrent flow through the current sensitive relay 139 to actuate it. Asthe vehicle slows, however, and the armature voltage of the left wheelmotor 17 decreases, a sufficient current willflow via the diode in leg175, through the wheel motor 17 and through the current sensitive relay139 to cause its actuation. For example, it has been found satisfactoryto employ a circuit in which reversal is effected when armature voltageof a wheel motor decreases to the value of approximately 35 volts, voltsbeing taken up by components of the circuit, rendering the effectivebucking voltage only volts. Upon actuation of the current sensitiverelay 139, serving as a part of the actuation means 75, the reversingswitch means 53 and 61 will be actuated and the vehicle is set up forreverse motion.

After the vehicle has travelled in the reverse direction a desireddistance, the operator will signal forward operation by moving hiscontroller oppositely to the direction described hereinbefore.Accordingly, the switches 189a-c will be closed and the switches 187a-cwill be opened. Thus, the diode 137 will be connected via buckingterminal 165 with the first main line bus 39 and the current sensitiverelay 139 will be connected via bucking terminal 167 with the outputterminal 181 of the bridge means 141. Again, when the slowest turningmotor attains a voltage low enough, a sufficient current will flowthrough the current sensitive relay 139 and actuate the reversing switchmeans 53 and 61 to set up the vehicle for forward operation.

In some applications it may be desirable, instead of sensing motorarmature voltage directly, to sense a voltage which is a function of themotor armature voltage, as for example, the voltage drop across aresistance grid means. Further, if desired, a solid state gating devicecould be utilized instead of the current sensitive relay, in which casethe result of the voltage of the regulated voltage source and thatapplied to bucking terminals 165, 167 would be used to control thetriggering of the gating device.

General From the foregoing description and drawings, it can be seen thatthis invention provides an improved reversing control system for anelectrically powered vehicle. In one aspect of the invention, thereversal of the vehicle is effective in response to speed of movement ofthe vehicle, as sensed from at least one wheel. In another aspect of theinvention, the speed of the vehicle is sensed from at least two wheelsdisposed on opposite sides of the vehicle so as to obtain uniformity ofresponse of the reversal of the vehicle, regardless of whether thevehicle is moving straight ahead or turning in one direction or theother. In a further aspect of the invention, the speed sensing meanscomprises a voltage sensing means and a circuit in which the armaturevoltages of two wheel motors are connected in bucking relationship witha regulated voltage source so as to effeet a sufficient flow of currentto actuate a current sensitive relay when the armature voltage of theslowest turning wheel motor drops below a predetermined voltage. Theinvention herein disclosed accomplishes the objects delineatedhereinbefore and satisfies the needs which the prior art has notsatisfied.

It will be understood that the showing of the respective blocks,switches, relays, controllers, power sources and the like are schematiconly and may be modified invarious ways as will be apparent to thoseskilled in the art, without departing from the principles of theinvention. Thus, the foregoing disclosure and the showings made in thedrawings are merely illustrative of the principles of this invention andare not to be interpreted in a limiting sense.

What is claimed is:

1. A control system for an electrically powered, selfpropelled vehiclecomprising in combination:

a. a prime mover power source;

b. a direct current generator having a shunt field;

c. means for supplying excitation to said generator shunt field;

(1. means mechanically coupling said generator to said power source;

e. a direct current electric drive motor having a shunt field and aseries field;

f. conductor means operably connecting output terminals of saidgenerator with input terminals of said motor;

g. means for supplying excitation to said motor shunt field;

h. means, including a controller, connected with said generatorexcitation means for signalling direction and speed of said vehicle bysignalling the polarity and magnitude of power to be supplied from saidgenerator to said motor;

i. means connected with said motor excitation means for signalling themagnitude of excitation to be supplied to said motor shunt field;

j. reversing switch means for effecting reversal of said motor seriesfield connections immediately prior to reversal of direction of saidvehicle so as to maintain the desired direction of current flow throughsaid series field;

k. actuation means connected with said reversing switch means foractuating said reversing switch means;

1. means for deriving a voltage signal which is a function of thearmature voltage of said motor and utilizing said signal to effectactuation of said actuation means when the speed of said motor decreasesto or is below a predetermined speed.

2. A control system for an electrically powered, selfpropelled vehiclecomprising in combination:

a. a prime mover power source;

b. a direct current generator having a shunt field;

c. means for supplying excitation to said generator shunt field;

d. means mechanically coupling said generator to said power source;

e. a plurality of direct current electric wheel drive motors each havinga shunt field and a series field;

f. conductor means operably connecting output terminals of saidgenerator with input terminals of said wheel motors;

g. means for supplying excitation to said wheel motor shunt fields;

h. means, including a controller, connected with said generatorexcitation means for signalling direction and speed of said vehicle bysignalling the polarity and magnitude of power to be supplied to saidwheel motors;

i. means connected with said motor excitation means for signalling themagnitude of excitation to be supplied to said wheel motor shunt fields;

j. reversing switch means for effecting reversal of said respectivemotor series field connections immediately prior to reversal'ofdirection of said vehicle so as to maintain the desired direction ofcurrent flow through said series field;

k. actuation means connected with said reversing switch means foractuating said reversing switch means;

1. means for deriving a voltage signal which is a function of thearmature voltage of one of said motors and utilizing said signal toeffect actuation of said actuation means when the speed of said motordecreases to or is below a predetermined speed.

3. A control system for an electrically powered, selfpropelled vehiclecomprising in combination:

a. a prime mover power source;

b. a direct current generator having a shunt field;

0. means for supplying excitation to said generator shunt field;

d. means mechanically coupling said generator to said power source;

e. a plurality of direct current electric wheel drive motors each havinga shunt field and a series field;

f. conductor means operably connecting output terminals of saidgenerator with input terminals of said wheel motors;

g. means for supplying excitation to said wheel motor shunt fields;

h. means, including a controller, connected with said generatorexcitation means for signalling direction and speed of said vehicle bysignalling the polarity and magnitude of power to be supplied to saidwheel motors;

i. means connected with said motor excitation means for signalling themagnitude of excitation to be supplied to said wheel motor shunt fields;

j. reversing switch means for effecting reversal of said motor seriesfield connection immediately prior to reversal of direction of saidvehicle so as to maintain the desired direction of current flow throughsaid series field;

k. actuation means connected with said reversing switch means foractuating said reversing switch means;

1. means connected with at least two wheel motors,

one on each side of said vehicle for deriving respective voltage signalswhich are a function of the armature voltage of respective said lastmentioned motors, and utilizing said signals to effect substantiallyuniform actuation of said actuation means when the speed of a said wheelmotor decreases below a predetermined speed, regardless of whether saidvehicle is turning in either direction or moving straight ahead.

4. A control system for an electrically powered, selfpropelled vehiclecomprising in combination:

a. a prime mover power source;

b. a direct current generator having a shunt field;

c. a first means for supplying excitation to said generator shunt field;I d. second means mechanically coupling said generator to said powersource;

e. a plurality of direct current eletric wheel drive motors each havinga shunt field and a series field;

f. third means comprising conductor means operably connecting outputterminals of said generator with input terminals of said wheel motors;

g. fourth means for supplying excitation to said wheel motor shuntfields;

h. fifth means, including a controller, connected with said generatorexcitation means for signalling direction and speed of said vehicle bysignalling the polarity and magnitude of power to be supplied to saidwheel motors;

. sixth means connected for signalling the magnitude of excitation to besupplied to said wheel motor shunt fields;

j. reversing switch means for effecting reversal of said respectivemotor series field connections immediately prior to reversal ofdirection of said vehicle so as to maintain the desired direction ofcurrent flow through said series field;

k. actuation means connected with said reversing switch means foractuating said reversing switch means; said actuation means comprising acurrent sensitive relay operable when a current greater than apredetermined minimum current flows therethrough;

1. means connected with at least two wheel motors,

one on each side of said vehicle for deriving respective voltage signalswhich are a function of the armature voltage of respective said lastmentioned motors, and utilizing said signals to effect substantiallyuniform actuation of said actuating means when the speed of a said wheelmotor decreases below a predetermined speed, regardless of whether saidvehicle is turning in either direction or moving straight ahead; saidspeed responsive means comprising:

i. a regulated voltage power source that is connectable in buckingrelationship with the voltage drop across said wheel motors; said wheelmotors being connected in parallel; said regulated voltage power sourcebeing adapted to supply a voltage greater than the sum of the voltagedrop across a respective wheel motor at said predetermined speed and thevoltage drop across said current sensitive relay when said predeterminedminimum current flows therethrough;

ii. unidirectional conductor means serially connected with saidregulated voltage source and said current sensitive relay;

iii. bridge means for selecting the slowest turning wheel motor to beserially connected with said regulated voltage power source and saidcurrent sensitive relay; said bridge means having four legs, respectivesides of said bridge means comprising two adjacent legs having an inputterminal that is serially connected with a respective said wheel motor;a first leg of said adjacent legs having a unidirectional conductormeans for permitting current to flow in one direction with respect tosaid input terminal and the second of said adjacent legs having aunidirectional conductor means for permitting current to flow in theother direction with respect to said input terminal; the juncture ofsaid first legs of said sides defining a first output terminal, and thejuncture of said second legs of said sides defining a second outputterminal; and

iv. switch means for maintaining said regulated voltage power sourceconnected in a signalled bucking relationship with said wheel motorsregardless of the direction of travel of said vehicle; said switch meanscomprising a first group of switches responsively connected with saidfifth means for serially connecting a first output terminal of saidbridge means, said wheel motors, said regulated voltage power source,and said current sensitive relay for current flow in one directionthrough said wheel motors; and a second group of switches responsiveiyconnected with said fifth means for serially connecting a second outputterminal of said bridge means, said wheel motors, said regulated voltagepower source, and said current sensitive relay for current flow in asecond direction through said wheel motors.

S. The control system of claim 4 wherein said regulated voltage powersource, said unidirectional conductor, and said current sensitive relayare serially connected with a pair of bucking terminals; and whereinsaid switch means comprises three pair of contacts, only one contact ofeach said pair being closed at a time; one pair of said contacts beingdisposed intermediate and connected with said pair of bucking terminalsand one side of said regulated voltage power source; a second pair ofsaid contacts being disposed intermediate and connected with said pairof bucking terminals and the other side of said regulated voltage powersource; and the third pair of said contacts connected with one of saidbucking terminals and the respective output terminals of said bridgemeans, one contact of said third pair being connected with one outputterminal and the other contact of said third pair being connected withthe other output terminal; said other bucking terminal being connectedwith the sides of said wheel motors opposite to the sides that areconnected with respective input terminals of said bridge means.

1. A control system for an electrically powered, self-propelled vehiclecomprising in combination: a. a prime mover power source; b. a directcurrent generator having a shunt field; c. means for supplyingexcitation to said generator shunt field; d. means mechanically couplingsaid generator to said power source; e. a direct current electric drivemotor having a shunt field and a series field; f. conductor meansoperably connecting output terminals of said generator with inputterminals of said motor; g. means for supplying excitation to said motorshunt field; h. means, including a controller, connected with saidgenerator excitation means for signalling direction and speed of saidvehicle by signalling the polarity and magnitude of power to be suppliedfrom said generator to said motor; i. means connected with said motorexcitation means for signalling the magnitude of excitation to besupplied to said motor shunt field; j. reversing switch means foreffecting reversal of said motor series field connections immediatelyprior to reversal of direction of said vehicle so as to maintain thedesired direction of current flow through said series field; k.actuation means connected with said reversing switch means for actuatingsaid reversing switch means; l. means for deriving a voltage signalwhich is a function of the armature voltage of said motor and utilizingsaid signal to effect actuation of said actuation means when the speedof said motor decreases to or is below a predetermined speed.
 2. Acontrol system for an electrically powered, self-propelled vehiclecomprising in combination: a. a prime mover power source; b. a directcurrent generator having a shunt field; c. means for supplyingexcitation to said generator shunt field; d. means mechanically couplingsaid generator to said power source; e. a plurality of direct currentelectric wheel drive motors each having a shunt field and a seriesfield; f. conductor means operably connecting output terminals of saidgenerator with input terminals of said wheel motors; g. means forsupplying excitation to said wheel motor shunt fields; h. means,including a controller, connected with said generator excitation meansfor signalling direction and speed of said vehicle by signalling thepolarity and magnitude of power to be supplied to said wheel motors; i.Means connected with said motor excitation means for signalling themagnitude of excitation to be supplied to said wheel motor shunt fields;j. reversing switch means for effecting reversal of said respectivemotor series field connections immediately prior to reversal ofdirection of said vehicle so as to maintain the desired direction ofcurrent flow through said series field; k. actuation means connectedwith said reversing switch means for actuating said reversing switchmeans; l. means for deriving a voltage signal which is a function of thearmature voltage of one of said motors and utilizing said signal toeffect actuation of said actuation means when the speed of said motordecreases to or is below a predetermined speed.
 3. A control system foran electrically powered, self-propelled vehicle comprising incombination: a. a prime mover power source; b. a direct currentgenerator having a shunt field; c. means for supplying excitation tosaid generator shunt field; d. means mechanically coupling saidgenerator to said power source; e. a plurality of direct currentelectric wheel drive motors each having a shunt field and a seriesfield; f. conductor means operably connecting output terminals of saidgenerator with input terminals of said wheel motors; g. means forsupplying excitation to said wheel motor shunt fields; h. means,including a controller, connected with said generator excitation meansfor signalling direction and speed of said vehicle by signalling thepolarity and magnitude of power to be supplied to said wheel motors; i.means connected with said motor excitation means for signalling themagnitude of excitation to be supplied to said wheel motor shunt fields;j. reversing switch means for effecting reversal of said motor seriesfield connection immediately prior to reversal of direction of saidvehicle so as to maintain the desired direction of current flow throughsaid series field; k. actuation means connected with said reversingswitch means for actuating said reversing switch means; l. meansconnected with at least two wheel motors, one on each side of saidvehicle for deriving respective voltage signals which are a function ofthe armature voltage of respective said last mentioned motors, andutilizing said signals to effect substantially uniform actuation of saidactuation means when the speed of a said wheel motor decreases below apredetermined speed, regardless of whether said vehicle is turning ineither direction or moving straight ahead.
 4. A control system for anelectrically powered, self-propelled vehicle comprising in combination:a. a prime mover power source; b. a direct current generator having ashunt field; c. a first means for supplying excitation to said generatorshunt field; d. second means mechanically coupling said generator tosaid power source; e. a plurality of direct current eletric wheel drivemotors each having a shunt field and a series field; f. third meanscomprising conductor means operably connecting output terminals of saidgenerator with input terminals of said wheel motors; g. fourth means forsupplying excitation to said wheel motor shunt fields; h. fifth means,including a controller, connected with said generator excitation meansfor signalling direction and speed of said vehicle by signalling thepolarity and magnitude of power to be supplied to said wheel motors; i.sixth means connected for signalling the magnitude of excitation to besupplied to said wheel motor shunt fields; j. reversing switch means foreffecting reversal of said respective motor series field connectionsimmediately prior to reversal of direction of said vehicle so as tomaintain the desired direction of current flow through said seriesfield; k. actuation means connected with said reversing switch means foractuating said reversing switch means; said actuation means comprising acurrent sensitive Relay operable when a current greater than apredetermined minimum current flows therethrough; l. means connectedwith at least two wheel motors, one on each side of said vehicle forderiving respective voltage signals which are a function of the armaturevoltage of respective said last mentioned motors, and utilizing saidsignals to effect substantially uniform actuation of said actuatingmeans when the speed of a said wheel motor decreases below apredetermined speed, regardless of whether said vehicle is turning ineither direction or moving straight ahead; said speed responsive meanscomprising: i. a regulated voltage power source that is connectable inbucking relationship with the voltage drop across said wheel motors;said wheel motors being connected in parallel; said regulated voltagepower source being adapted to supply a voltage greater than the sum ofthe voltage drop across a respective wheel motor at said predeterminedspeed and the voltage drop across said current sensitive relay when saidpredetermined minimum current flows therethrough; ii. unidirectionalconductor means serially connected with said regulated voltage sourceand said current sensitive relay; iii. bridge means for selecting theslowest turning wheel motor to be serially connected with said regulatedvoltage power source and said current sensitive relay; said bridge meanshaving four legs, respective sides of said bridge means comprising twoadjacent legs having an input terminal that is serially connected with arespective said wheel motor; a first leg of said adjacent legs having aunidirectional conductor means for permitting current to flow in onedirection with respect to said input terminal and the second of saidadjacent legs having a unidirectional conductor means for permittingcurrent to flow in the other direction with respect to said inputterminal; the juncture of said first legs of said sides defining a firstoutput terminal, and the juncture of said second legs of said sidesdefining a second output terminal; and iv. switch means for maintainingsaid regulated voltage power source connected in a signalled buckingrelationship with said wheel motors regardless of the direction oftravel of said vehicle; said switch means comprising a first group ofswitches responsively connected with said fifth means for seriallyconnecting a first output terminal of said bridge means, said wheelmotors, said regulated voltage power source, and said current sensitiverelay for current flow in one direction through said wheel motors; and asecond group of switches responsively connected with said fifth meansfor serially connecting a second output terminal of said bridge means,said wheel motors, said regulated voltage power source, and said currentsensitive relay for current flow in a second direction through saidwheel motors.
 5. The control system of claim 4 wherein said regulatedvoltage power source, said unidirectional conductor, and said currentsensitive relay are serially connected with a pair of bucking terminals;and wherein said switch means comprises three pair of contacts, only onecontact of each said pair being closed at a time; one pair of saidcontacts being disposed intermediate and connected with said pair ofbucking terminals and one side of said regulated voltage power source; asecond pair of said contacts being disposed intermediate and connectedwith said pair of bucking terminals and the other side of said regulatedvoltage power source; and the third pair of said contacts connected withone of said bucking terminals and the respective output terminals ofsaid bridge means, one contact of said third pair being connected withone output terminal and the other contact of said third pair beingconnected with the other output terminal; said other bucking terminalbeing connected with the sides of said wheel motors opposite to thesides that are connected with respective input terminals of said bridgemeans.